Adding an aromatic residue to the transmembrane cavity increases affinity for TEA⁺. (A) Typical currents through Kir1.1 N152Y channels in inside-out patches with 110 mM K⁺ on the outside and 110 mM K⁺ with and without 0.05 mM TEA⁺ on the inside of the patch. Currents are shown at −100 and +100 mV. (B) Analysis of P_o in the absence and presence of TEA⁺ (two to five measurements per point). (C) i-V relationships with and without TEA⁺. (D) Voltage dependence analyzed using Eq. 3 with P_o substituted for i for [K⁺]_o = 110 and 11 mM. Values of K_i(0) were 0.37 mM ([K⁺]_o = 110 mM) and 0.11 mM ([K⁺]_o = 11 mM). Values of zδ were 0.82 ([K⁺]_o = 110 mM) and 0.84 ([K⁺]_o = 11 mM).